Yes, it's a bit of a minefield because there are so many variations and combinations of vowels just in the UK alone.

Another interesting feature is the rhotic 'r' [ɹ] as in pronouncing the 'r' in 'water'. It is the biggest difference between the British and American accent. The rhotic 'r' is only found in Scotland, Ireland and the West Country but four hundred years ago it was common almost everywhere; hence its prevalence in the US and Canada today. E.g. [ɜ:] bird (UK) and [ɝ] bird (US).